Reliable clinical distinctions in highly trained competitive athletes between physiologically-induced morphologic changes ("athlete heart") and hypertrophic cardiomyopathy is often difficult. It would appear from recent data that left ventricular wall thicknesses of 16 mm are incompatible with athlete heart. Also Doppler echocardiographic assessment of left ventricular filling may aid in resolving the differential diagnosis of these two conditions, in that filling patterns are virtually always nodal in athletes with wall thickening and abnormal in 80% of patients with mild morphologic expressions of hypertrophic cardiomyopathy.